Lecture AP Biology Chapter 36 Resource acquisition and transport in vascular plants

Ch. 36 Warm-Up
1.

Describe the process of how H2O gets into
the plant and up to the leaves.

2.

Compare and contrast apoplastic flow to
symplastic flow.

3.

Explain the mass flow of materials in the
phloem (source to sink).


Ch. 36 Warm-Up
1.

What is transpiration?

2.

What are mycorrhizae?

3.

What is the function of the Casparian strip?

Chapter 36
Resource Acquisition and Transport in Vascular Plants


What you need to know:






The role of passive transport, active transport,
and cotransport in plant transport.
The role of diffusion, active transport, and bulk
flow in the movement of water and nutrients in
plants.
How the transpiration cohesion-tension
mechanism explain water movement in plants.
How pressure flow explains translocation.


What does a
plant need?


Review:
 Selectively permeable membrane: osmosis,
transport proteins, selective channels
 Proton pump: active transport; uses E to pump
H+ out of cell  proton gradient

 Cotransport: couple H+ diffusion with sucrose
transport
 Aquaporin: transport protein which controls
H2O uptake/loss


Solute transport
across plant cell
plasma membranes


Osmosis
**Water potential (ψ): H2O moves from high ψ 
low ψ potential, solute conc. & pressure
◦ Water potential equation: ψ = ψS + ψP
◦ Solute potential (ψS) – osmotic potential
◦ Pressure potential (ψP) – physical pressure on
solution
◦ Pure water: ψS = 0 Mpa
◦ Ψ is always negative!
◦ Turgor pressure = force on cell wall
 Bulk flow:
flow move H2O in plant from regions of high
 low pressure
** Review AP Bio Investigation 4








Flaccid: limp (wilting)
Plasmolyze: shrink, pull away from cell wall (kills
most plant cells) due to H2O loss
Turgid: firm (healthy plant)

Turgid Plant Cell

Plasmolysis


A watered impatiens plant regains its turgor.


Vascular Tissues: conduct molecules
Xylem

Phloem

Nonliving functional

Living functional

Xylem sap = H2O &
minerals

Phloem sap = sucrose,
minerals, amino acids,
hormones

Source to sink
(sugar made) to (sugar
consumed/stored)


Transport of H2O and minerals into xylem:
Root epidermis  cortex  [Casparian Strip] 
vascular cylinder  xylem tissue  shoot system


At Root Epidermis



Root hairs: increase surface area of absorption
at root tips
Mycorrhizae: symbiotic relationship between
fungus + roots
◦ Increase H2O/mineral absorption

The white mycelium of the fungus
ensheathes these roots of a pine tree.


Transport pathways across Cortex:



Apoplast = materials travel between cells
Symplast = materials cross cell membrane, move

through cytosol & plasmodesmata


Entry into Vascular Cylinder:


Endodermis (inner layer of cortex) sealed by
Casparian strip (waxy material)
◦ Blocks passage of H2O and minerals
◦ All materials absorbed from roots enter xylem
through selectively permeable membrane
◦ Symplast entry only!


How does material move vertically (against gravity)?
Transpiration:
Transpiration loss of H2O via
evaporation from leaves into air
Root pressure (least important)

1.


Diffusion into root pushes sap up

2.

Cohesion-tension hypothesis

◦

◦

Transpiration provides pull
Cohesion of H2O transmits pull from
rootsshoots



Guttation: exudation of water droplets seen in
morning (not dew), caused by root pressure


Stomata regulate rate of transpiration



Stomata – pores in epidermis of leaves/stems, allow gas
exchange and transpiration
Guard cells – open/close stoma by changing shape
◦ Take up K+  lower ψ  take up H2O  pore opens
◦ Lose K+  lose H2O  cells less bowed  pore closes





Cells stimulated open by: light, loss of CO2 in
leaf, circadian rhythms
Stomata closure:
closure drought, high temperature,

wind


BIOFLIX: WATER TRANSPORT
IN PLANTS


Sugar Transport






Translocation: transport of sugars into phloem
by pressure flow
Source  Sink
◦ Source = produce sugar (photosynthesis)
◦ Sink = consume/store sugar (fruit, roots)
Via sieve-tube elements
Active transport of sucrose


Bulk flow in
a sieve tube


Symplast is dynamic



Plasmodesmata allows movement of RNA &
proteins between cells
Phloem can carry rapid, long-distance electrical
signaling
◦ Nerve-like function
◦ Swift communication
◦ Changes in gene expression, respiration,
photosynthesis